Add AuthenticationFailureListener.

guacamole-ext/src/main/java/net/sourceforge/guacamole/net/event/listener/AuthenticationFailureListener.java

@@ -0,0 +1,24 @@
+package net.sourceforge.guacamole.net.event.listener;
+
+import net.sourceforge.guacamole.net.event.AuthenticationFailureEvent;
+
+/**
+ * A listener whose postAuthenticationFailure() hook will fire immediately
+ * after a user's authentication attempt fails. Note that there is no
+ * preAuthenticationFailure() hook - authentication failure cannot be canceled,
+ * it can only be observed after the fact.
+ * 
+ * @author Michael Jumper
+ */
+public interface AuthenticationFailureListener  {
+   
+    /**
+     * Event hook which fires immediately after a user's authentication attempt
+     * fails.
+     * 
+     * @param e The AuthenticationFailureEvent describing the authentication
+     *          failure that just occurred.
+     */
+    public void postAuthenticationFailure(AuthenticationFailureEvent e);
+    
+}